Stereodisp arator



Nov. 14, 1944. s. RENSHAW STEREODI SPARATOR Filed Dec 22 1941 \6 Sheets-Sheet 1 m i i INVENTOR SAMUEL nENsHAw BY 1 fa MM ATTORNEYS 1944- s. RENSHAW 2,36 7

S TEREO-DI SPARATOR Filed Dec. 22, 1941 6 Sheets-Sheet 2 INVENTOR SAMUEL RENSHAW H I I H 3 BY ATTORNEY 9 s. RENSHAW v STEREO -DISPARATOR Filed Dec. 22, 1941 6 Sheets-Sheet 5 INVENTOR SAMJEL QENSHAW ATTORNEYS Nov. 14, 1944. a RENSHAW 2,362,857

STEREO-DI ISPARATVOR ,F'iled Dec. 22, 1941 6 Sheets-Sheet 4 UDUUDDUUDUU U NOV. 14, 1944. RENSHAW STEREO-DISPARATOR Filed D86. 22 1941 6 Shepts-Sheet 5 IWEN'IDR SAMUEL QEJSHAW Nov. 14, 1944. I s. RENSHAW 2,362,857

STEREO-'DISPARATOR Filed Dec. 22, 1941 6 Sheets-Shet e Patented Nov. 14, 1944 UN TE STAT Samuel ltenshaw,

The Ohio State Unlv t i Foundation, Columbus, Ohio, a corporation oi Ohio Application December 32, 1941, Serial No. 424,001 Claims. (cl. sa-zo') The present invention relates to methods of testing visualacuity and instruments for carrying out these methods, and more particularly to the examination of the eyes for refractive defects, excessive phoria, and conditions involving ocular image diii'erences and departures from. normal stereoscopic or tri-dimensional vision.

The primary object of the invention is to provide an improved method and apparatus for testing visual perception, particularly as applied to binocular or stereoscopicvision', Another object is to provide improved methods and devices for determining vertical and lateral phorias so as to test the prismatic imbalance, both vertically and laterally, of a pair of eyes.

Still another object is to provide an instrument which is designed more especially for depth perception, and in which the stereoscopic resultmay be obtained in the form of a reading on a scale or scales, according to the adjustment of independent targets or viewing charts.

Another object is to provide an instrument, in ,which the stereoscopic pictures or charts are independently mounted as contrasted with a single mounting of the prior art,

A further object is to provide an improved instrument which presents to the two eyes, pairs of half-stereograms by means of which the correct optical positions in space for true stereopsis are attained.

Other objects are to provide an improved device which automatically produces a new, correct setting of these relations for attaining true stereopsis for each change in the focal length of the lens system; a device and methods for measuring the apparent-size of objects, and of determining the size constancy index for any observer; an instrument of the character described which may be attached to any standard refracting head or turret or to any stereoscopic apparatus, thereby enabling an examiner to ,secure measurements of greater constancy .and accuracy than are possible with the use of existing stereometric instruments, in which the target separations are held constant throughout the focal range; a means of measuring the limits in terms of the length of the principal focus of the lens system within which an observer can maintain single binocular three-dimensional vision; a' device and methods for the orthoptic training and improving of stereoscopic visual skills and the measurement of the amount of such improvement; a devicewhich when. used with stereograms prepared according to the same principle -may be used to measure perceptual.form, position or visual apparent movement as well-as apparent size.

Reference should now be made to the following description and the accompanying drawings; r

In the drawings:

Figure 1 is a view lookin down on the improved stereoscopic devioe.

Figure 2 is a diagram useful in explaining some of the principles on which the device operates.

Figure 3 is an end view of the device looking at about the position indicated by the line 3-1 (Figure 4) in the direction of the arrows.

Figure 4 is an enlarged perspective front and top view of the improved instrument, .withthe left-hand stereogram broken away to show in detail the elements at the rear.

Figure 5-is a cross ing device provided at the outside lower edges of each stereogram for charts in a lateral direction, hereinafter. This section is 5-5 in Figure 4. y

Figure 6 is a fragmentary sectional view, somewhat enlarged, of the slot and projection arrangement forguiding the charts in the vertical direction. This view is 6-6 in Figure 4.

Figure 7 is a top plan view 0! the improved instrument, and Figure 8 is a bottom view.

Figure 9 shows a front view'of the instrument, looking at about the position of the line 9-9 in Figure "I.

Figure 10 depicts a chart on which a number of phenomenal-areas appear, indicated as rectangles, which chart may be used in determinas will be explained taken along the line ing defects of stereoscopic vision.

Figure 11 is a graph by which the determinations found in the laboratory and employing the improved instrument may be translated into field test measurements.

Figure 12 is a photograph which shows a subject in the act of drawing the phenomenal size of a target which can be seen in the background.

Figure 13 is a view somewhat similar to Figure 12, except that the target. has been moved farther away from the subject, necessitating a reduction in the phenomenal area.

The principle '0} the invention The stereoscopic law, based purely upon con- .sideration of geometricoptics, is stated as follows':

or thestereo-parallax 'x=distance from the eye ofon r a=distance from the -.iection' Y 2b=the interocular distance sectional view of a clamp- I the purpose of moving the taken along the line the point of flxa ,eye of the p n r stereoscopic resolution.

In order to provide the correct separation of stereo-targets, at a specified distance and viewed through lenses of specified spherical or prismatic power to produce the best possible fusion (1. e. binocular single three-dimensional discrimination), it is necessary to diminish the separation measurement of changes in the apparent size of any test objector target which accompany of the two targets as the focal length is changed lustrated by the diagram shown in Figure 2, to U which reference is now made. 0 and. O represent the optical centers of the stereo-viewing lenses, and Op and O'q the principal axes of these two lenses. The distance OF is the principal focus of the lenses, with the point F denoting infinity and the point N the near point. K is the septum of any stereoscopic viewer and the line PA is the stereo-axis. From the equation given hereinbefore, it may be shown that if the eyes are emmetropic two similar images at the points p and q in the diagram will be projected upon the retinas in such a position as to produce the opportunity for best possible fusion. When the focal length of the system has been changed so that the stereo-targets are now viewed at position O'N, the points p and q. in order to produce the same efiectivesingle binocular vision.

must now be moved to positions 1-, 8' instead of p .q'. Points on the line Pp and Pa describe the correct positions of similar stereogram points for optical fusion.

The angle 0 in the diagram thus defines the relative correct positions of the targets in terms of any specified lens power of the decentered spheres or prisms. In the original model of this apparatus +5 diopter split spheres of 200 mm. focal-length were used. In this case the angle 6 was determined to be 26 i0. Means is provided so that for lens power of any other focal length, proper adjustment of this angle can be made so as to maintain the appropriate conditions for best possible fusion. Provision is also made so that the targets may be transparencies ofany sort or opaque stereograms to be viewed by reflected light. 7

The improved apparatus and methods which will be described in detail hereinafter, combine a device for measuring stereopsis by the utilization both of geometric optical principles and an objective measure of phenomenal psychological size, form, position and distance relations.

'It makes possible the determination of the limits .within which fusion can be maintained for test objects or targets of different intrinsic design properties. Stereoscopic vision is a dynamic function'in which the properties of figure-ground patterning or structuring is an important determinant of the skill possessed by any observer for Existing sterecmetric devices make no provision for the measurement of this'factor. Y

The apparatus when used with the psychophysical method of equivalents provides fo t e changes in the focal length of the lens system. This may be defined as the combination of the viewing lens or lenses together with those of the observer's own eyes. This is of great importance. Anything which changes the apparent size of a test object changes also the limits of resolution and discrimination of that object. ,This becomes a principle of first order importance in several measurements, 1. e. visual acuity, etc., which are used as the basis for proper corrective lens prescription. The apparatus may be used in con- Junction with rotary prisms or other accessory lens devices as an orthoptic instrument for theexercise and training of accommodation, and for the development of stereoscopic skill. It has long been recognized (von Frey) that the perception oi depth and distance is not determined by visual factors alone. Proof of this fact is seen in the hundreds of cases of aphakias when cataracts have been surgically removed, thus restoring sight. In all such cases thepatient has had to learn to see in the third dimension. There is additional evidence that children below the age of five or six show a normal micropsia; Objects are normally seen smaller than they really are.

However, a good many adult presons may have the same eyesight tendency as children, and in other cases the adults may actually have vision which causes them to see objects'much larger than they really are. The same discrepancies as to position and shape of the object may occur r in all of these cases.

The apparatus and methods set forth hereinafter provide an instrument for the ophthalmological and optometric determination of the amount and kind of such visual functions and thereby provide an important check upon any prescribed lens correction intended to give more comfortable and effective vision. A measurement with this apparatus and methods made before the fitting of the correction, and another such measurement made after the patient has become accustomed to his new lenses, will reveal the extent to which such correction has accomplished the purpose of providing the closest possible approximation to emmetropic vision. This apparatus and these methods make possible the genetic study of the development of stereopsis from early childhood to adulthood; This apparatus and methods provide a device which may be used by the military establishments of our country for the selection and training of persons suitable to operate binocular devices such as range finders, spotters, gun pointers and the like. The numerical determinations provided by the improved iiiposure and the hue saturation and brightness of the incident light. With this addition this apparatus makes it possible to determine the limits within which the reciprocity law operates in stereoscopic vision, and this in turn, permits the specification of the time-size-intensity, distance and figure-ground relations for optimum stereopsis.

General construction The improved instrument is shown more particularlyin Figures 1, 3, 4, 7, 8 and 9. This instrument may conveniently constitute an attachment for any suitable and well known type of binocular arrangement, and in Figure 1 this arpie, by means of a I. beam. This 1 gets-or vided an upright metalholder 23, constituting a- 7 having a downwardly extendthin metal'plate I 24 atthe top,'.an d provided ving 'U-s'haped loop with'a flange 25 I j to'the plate Ziin any suitable manner, for exam- Qple by rivets 26. v I tending brackets i3 (Figure 3) may be employed to. maintain .the'holder iposition. vThe holder assassv rangement has been indicated by the light lines to distinguish the old apparatus from the improved attachment or instrument which is shown in heavy lines. In general, the old binocular structure may comprise a heavy base I with an arm 2 pivotally mounted at 3, and having a clamping adiustment indicated at l. The arm 2 may take the form or a g'ooseneck, and at its um! andcarries a pair viewing cylinders I, with appropriate lenses contained in supporting elements indicated at I. The eye shield I may be provided at each side, and also arrest 3 at the middle against which the patient presses his forehead. The improved'attachment or instrument is carried on a horizontally extendin beam 3, preterablyoi rectangular section, and made of metal or or any other tough material, such as reinforced plastic and some oi the heavy, non- .warpable'woods. Q-Thebeam-I'is secured in any suitable manner tdthe, lower surfacesoi the cylinders 5, and ex- -t'ends 'infgeneral along. the median line or the of rectangular openings 21, spaced apart as two cylinders considered as a whole. At the end farthest away'irom the cylinders 5 the beam or j rod is provided with 'a transversely extending arm s, securedirigidly'to the beam, as for examportion I I which is bent upwardly (Figure 1) .and tightly embraces the sides of the beam 9. There is a pair or angularly extending'bars I2 pivotally mounted, asindicated at I 3, on the ends 01- the arm I II, thesebars extending for axconsiderable distance along the beam 3 and terminating at their farthest ends in tapered portions 1 I4, which aligns their inner edges with the sides or the beam. A tension" spring I3 is provided at the ends it of the bars I2, this spring serving to bring the ends I4 of the I bars together, as can be readily seen in Figure 8.

The bars I2, at their pivots I3, may rest on surfaces I6, countersunk in the upper surface of the arm III (Figure 1). There'is a screw I1 extending transversely of the bars I2, the screw being supported at the middle by a hollow lug I3 which loosely receives the screw. The latter is threaded at each end, as shown in Figure 8. and the threaded ends are received in threaded apertures formed by the lugs I9 which are secured to the under sides of the bars I2. The screw I'I terminates at one,end in a knurled knob 20. The threaded portions of the screws H are threaded in opposite directions so that when the knob 20 is turned in one direction the bars I2 may be caused to swing outwardly at their pivots I3 to stretch the spring I5. Thus the angle which the bars I2 make with the beam Sis correspondingly changed. The knob 20 is also adapted to be rota-ted in such direction that the bars I2 will swing inwardly, for purposes which will be explained hereinafter.

' The beam 9 slidably carries a plate 2I, of a general octagonal shape, and provided with a rectangular =slotted opening indicated at. 22,

, which flts about the beam 9. The plate'2l is therefore'adapted to slide along the length oi! the plate supports the-stereogr'am tarhartsf, and for this purposethere is pro-- r y V v U ,iromsheetimetal bentunto a U-shape to obtain rigidity and h'aVing tapered'lower edges as shown 3, by i which to receive I an' upright boss 05 is provided; with a threaded bore at thebottom which is'secured A number of 'diagonallyex- 23 in a, strictly vertical 23 is provided with a pair shown, and thepurpose of which is to admit light from the rear which may be produced by a duorescent tube 23, extending in the same direction as the holder. The tube 23 may be supported at each end on the brackets 23, secured to the holder as shown in Figure 3, and one, o! the brackets may contain the necessary contacts for making circuit connections with a pair of electric wires 3| ior energizing the tube. 'It is apparent that when the tube 23 is activated light therefrom will shine through the openings 21 .and will render brilliant any transparent or translucent chart, picture or figure which may be placed over the openings 21. In case the chart or figure is not of a self-supporting character it may be desirable to insert apiece of milk or translucent glass between the'picture and the opening. The

.target or picture, of which there are two contained within the holder 23, is indicated at 3 I, and as will be noted the upper edge of the picture extends to a position underneath the loop 24.-

Thepicturev or target is usually mounted on a rectangularpiece of stiff cardboard-which may J be either of a translucent oropaque character,

as will be described later.

scribed. Bearing loosely against the nearer side of the holder 23 thereis a 'pair of horizontally extending thin metal plates 32. These plates are provided with tabs 33 which; extend awayirom the observer (Figure 4) and areadapted to slide ,in vertical openings 34 which areiprovided at the four places in the holder 23, two of these posi-' I tions being at opposite ends of the holder-and the othertwonear the middle of the h'olden The I I1 purpose of the tabs 33 and the openings 34'is to I align the plate 32 in a horizontal direction and to permit the plate to move in a vertical direcv tion,.as will be explained presently. The tabs 33 may be provided integralwith the plate32 by merely bending the horizontal tab portion out of line with the remaining portion of the plate.

- The vertical openings 34in the holder 23 are bounded by flangesat the upper and lower ends,

as indicated at 35, these-flanges being conveniently formed by bending small tab-like portions of the holder 23 out of line with the remaining vertical portions of the holder. It is apparent that the plate 32 is constrained to move in a vertical direction through a distance represented by the space between each tab'33 and the adjacent flange 35 (see l igurexb), The plate 32 carries an inverted S-shaped member '36 having a, flange 31 which is secured to the plate 32 and terminating at its upper end in a flange 38 (Figure 6),

which together with the plate 32, forms a trou h extending over the whole length of the plate 32.,

. in Figure? 1 ,uplir'ieiid I. f WaShG Z SJ spaced apart to receive the outer endf f a braickje t 5', and pinned to the screwi'as "in ted {a 46 The screw-42,3 also'provid'e'd" The picture or diagram 3| restsin this troughshaped space. v

There is a bracket-.39 extending through each V ic'ally extending screw 42. ,The he' screw -fly is provided with thick of similar construction to the bracket 39 so that the washers 43, 44 can bear against the horizon tal fiat portion of the bracket. The latter is secured in any suitable manner tothe holder 23 so that when the knob 41 is rotated the screw 42 is caused to turn, and inasmuch as the upper portion of the screw is fixed in space, due to the position of the washers 43, 44 and the bracket 45, the boss 4| will be caused to move either upwardly or downwardly, depending on the direction in which the knobis turned. .Thus the rotation of the knob 41 will cause the picture or chart 3| to move in the vertical direction, and each of these charts is provided with its own vertical-position adjusting knob 41. The purpose for this vertical adjustment will be explained when the optical properties of the instrument are described.

In case the cards 3| which bear the pictures are of an opaque character so that no light from the fluorescent tube 29 may be projected therethrough, it may be necessary to provide a light In addition to the vertical adjustment and in accordance with another feature of my invention, the cards 3| are permitted to and in most cases actually are caused to move in the horizontal direction, the arrangement :being such that the cards move in opposite directions with respect to one another, 1. e. either inwardly or outwith a knurled knob 41 The bracket 45 may be downwardly extending pin 6|, this pin being adapted to, slide through the slot 'in the bar 51 which is left open for a portion o'fitsv length by reason of the fact that the length of the plate 65 is considerably less than the length of the bar 51. The pin 6| is of a length suflicient to bear against the outside edges of the bars l2. In order to assure contact between the bar I2 and the pin 6|, a tension spring 62 is provided which is connected at one end to the inner'side of the metal piece 54 and at the other end to a small projection 63 which extends downwardly from the keeper plate 69: This spring, therefore, urges the metal piece 54 inwardly and in turn 'causes the rod 56 to move inwardly and therefore the pin 6| to contact the outside edges of the bars i2.

In order to move the plate 2| with respect to the beam 9, there is provided a downwardly extending hand grip member 64 (Figure 3) which is formed integral with the flanges 65 at each side of the plate 2|. A transversely extending pin 66 is carried by these flanges, this pin serving as a pivot axis for a lever 61 which has an upwardly extending tooth 69 bearing against the under side of the beam 9. .A compression spring 69 is positioned between the grip 64 and the lever 6?, this wardly as may be necessary. This horizontal movement is brought about by means of the following mechanism: Each card is provided atthe'lower outside edge with at least one vertical opening indicated at 53, ofwhich six such openings have been illustrated. In case more than one opening is provided the openings are preferably equidistantly spaced, and in order to prevent fraying at the edges a thin metal plate may be superposed on each card at the position of the openings, this plate having openings similar to those provided through each card. The purpose of each opening is to provide a grip on the card so as to force the latter either inwardly or outwardly. in the horizontal direction, as may be desired. This gripping effect is provided by an upright metal piece 54 having a central'groove to leave flanges at the outside, these flanges being provided with aligned threaded openings to receive a thumb screw 56 (Figure 5). This sc ew passes through one of the openings 53 in a card or chart.

For moving each metal piece 54 there is provided a rectangular bar 51 secured to the under side of the flange 25 and extending from the outer end of the flange as far as the nearest edge of the octagonal plate 2 l. Each bar 5'? is provided with a longitudinally extending slot for slidably receiving a rectangular rod 58 which is screwed at one end, as indicated at 59, to the upright piece 54. A keeper plate is secured to .the bottom side of the bar 51' and extends for only a limited length of the bar. The purpose of this plate .isfto retain the rectangular rod 59 in position." The. latter is provided at its inner end with a spring serving to urge the tooth 68 against the beam 9 and thus to produce friction at this point sufllcient to hold the plate 2| in place on the beam. In operation the fingers embrace the rear side of the grip 64 and the thumb is pressed against the lever 51, then by pushing or pullin the grip 64 the plate 2| can be moved with respect to the beam 9 either toward or away from the user of the instrument. Due to the fact that the pins 6| at both sides of the instrument contact their respective bars I2, any-movement of the plate 2| along the beam 9 will cause the cards 3| to move either outwardly or inwardly, depending on the direction in which the plate 2| is moved, and at a rate depending on the angle that the outside edges of the bars I 2 make with the central axis of the beam 9.

Consequently there is provided, in accordance with my invention, a simple but effective means by which the cards can be moved in the horizontal direction, either toward or away from one another, and at any desired rate depending on the taper provided by the outside edges of the bars l2. It has been explained that this taper may be adjusted by rotating the knob-20, which in turn causes an adjustment of the rate at which the cards 3| are moved either toward or away from one another as the plate 2| is moved longitudinally of the beam 9. It will now be apparent that the reason for providing more than one opening 53 is to accommodate the instrument to cards 3| of different lengths and thus to assure ,that the inner edges of the cards do not contact one another prior to the plate 2| having been moved to one of its extreme limits of travel. These openings are of an elongated shape so as to prevent binding at the screw 56 during the vertical movement of the cards. The upper surface of the beam 9 .is set off in graduations 10, for purposes .stops farthest removed from the lens mechanism 6. I

While various forms of pictures, charts or other insignia may be shown on the cards 3| there is double-lens camera the lenses of the phen board I target 3 a subject conditions existing-in th field can bereproduc'ed a I "target (Figure ing' 'through the pieces the same'im ;"actual v t; I I I I i lnormal stereoscopic", vi However} pati nt-1' illustrated, by way 0! example-, a topographical view which is similar to the field test picture shown in Figure 12.but without the subject. In

the corresponding field distances obtained from the graduations 10, the observer's eyes are tested throughout the desired range of distance. It

' the picture shown schematically on the cardNJ J5 has been pointed'out that the cards ii on which in Figure 9 reference numeral 12 indicates pref il the pictures are mounted will move toward one erably a white piece of cardboard which is set out in a field and supported above the ground as shown in Figure 12. The vertical lines 13 in Figure 9 schematically indicate the tree backgroundv shown inFigure 12, and the horizontal lines 14 schematically illustrate the contour of the field. It will be understood that the pictures shown on the cards 3| (Figure 9) are not exact duplicates but have been obtained by photographing the field, including the cardboard target 12, from a of which are spaced apart a distance corresponding to the average interocular distaiice.

In order to calibrate the instrument certain preliminary tests aregiven a subject 15' (Figure 1.12); who is assumed to have normal stereoscopic vision. This subject is -required to show on- .a

1 cha'rt 16 his impression of thepheno'menal size and shape of the cardboard square 12 1 views in the distance. I In '11 is setting out'on, a'chart 18 her impression omenal area'and shape of thecard- .19, which has'been .placedaat a .greater distance away from the observer. than inthecase of Figure rectangle drawn on the 1 the rectangle drawn on Figure 13 the subject 12. .It will be noted-that the chart 16 islarger than from the respective observers; Instead of drawin g rectangles shown on'charts- 16, 18,1(Figures. 12 andI"13)' .the subject may be requestedto ob-H serve lthe.-: distant cardb spectively, and to select from a large number .oi; ;Irectangles,v 'indicatediatch rt sh wn. insF eu 10, J-rectang'le which he} orishe believes cont oard targets 12, 1 9 re that ma marormsifto actually moved throughpredetermined distances ma e d' h e a n er own in- Figure *lo is .too large and. 1 another rectangle I and in that way makean -intelligenr selection. One of. the 1 rectangles shownin Figure 1011: considered: ;.to have the; proper phenomenal area-whens cardboard target ;12'or mal stereoscopicivision viewed by a subject of; nor

d 7 dispression, as

in the field;

;.assuming that he had may have nermai binocular; vision ,with :respect to anobject' placed. t a I fromthe observer,. butwhen the object 'iseither I moved farther ;awayI.-or

apredetermined-j distance sional vision fth'rou hou azidistance f rame fas n ar-p in the observer who 21 either towardor away from g the phenomenal" areas or.

80.? and. drawn -'on i the 'has been 1 v closer-to the observerthei I "patients vsteretiscofpi vision {would not be normal.'j--

It is thereforejfnecess made less was explained at length in connection with the optical diagram shown in Figure 2. The vertical movement of the cards 3| efi'ected at the knobs 41 allows for any prismatic imas aresult of field tests on the binocular vision 7 These curves have been. that he I "pression of the size of I the-v chart 18, due mainly x to the different distances that the cardboard 'tion.I In targets 12,19 are placed the; cardboar pieces Iii atpositions of the plate 2i which would correspond to the various curve a, and taking into ing power of the lenses.

mer ts for plotting "equation." FoLexample, the equation of a 111.1 t {l b employing phe om tWenty -Tnine year old male emmetrope is balance of the patients eyes: in the vertical direction.

1 Referring now to Figure 11, the curve a represents the plot of certaindeterminations found of a subject or patient, and curve b-represents corresponding, determinations resulting from tests performedon the same subject or patient 'the improved instrument. plotted against the logarithm of the phenomenal'area as the ordinate and the logarithm of the distance or the, viewed object in meters; 'I'he'various points marked c onthe' curve a were obtained by moving the target 12 (Figure 12) -from the observer when employing 15 throughout specified distances along the field .14 "and directing the observer to give his imthe'target at the various and as seen from the observers posidetermining the curve I) the same observer'orsubject is then requested to give his impression of the size of the phenomenal area of dtargets seen through the eyedistances field distances of the account the magnifythe instrument curve b are .5- r'eaIli 1;directly, from the graduations 10, since the I I I I movement'of the plate 21 away from the observer .1theylwalimpression:gainedasto -the phenome 1 servesQt LgiVe -]the same" optical effect in the 'overtheterrain. I I .It,iwillbefnotedthat the points obtained on curve-bfar'econsiderably less than the correpori'ding points obtained as the result of the order that the points on curve 17 'onioim to those actually obtained in the I liaise-points must be corrected by a cerfactor which .isexpressed as a mathematical In other words, everytwenty-nine year old male,

[having normal stereoscopic 'vision, which vision has been determined by the improved instru- I I ment'and represented by the curve b may have his instrum'entality :nieasured binocular vision .translated into actual field conditions'by the use .of th'e above noted formula It is apparent that .-only those persons having-normal stereo-vision :will show avisual index which conforms exactly to curve' b, and the variations in this index/as translated tolthe'field conditions, will Itell'ac- The distance measure- I be required to translate the instrument determinations expressed by the curve b into corresponding field determinations as expressed bythe curve a, take the case of a forty-nine year old male presbyope, this patient wearing the following lens correction:

The stereo-factor in this case is F=.09S+4.56, which is exactly two and one-half timesthe correction factor given in the previous case. Thus the improved instrument and methods are sufiiciently sensitive to reveal differences in the stereo-efliciency of individuals of varying ages and ocular conditions. These differences take into account the so-called "psychic convergence error so that this error can be measured and therefore controlled.

The quoted term refers to the fact that the mere awareness by an observer that he is look-. ing into an optical instrument of limited space compass prohibits the effective simulation of such factors as size and distance by means of such apparatus. This is a criticism of most existing stereometric devices. However, by the use of the improved instrument it can be predicted with great accuracy inthe omce or laboratory from the results obtained thereby, the sizes and distances phenomenally seen by an observer under real life conditions in the field without any visual adjuncts. This is very important because the improved instrument enables the ophthamologist or optometrist to determine by simple and convenient mean facts about a patients vision, with or without correction, which could only be a; and is equivalent to the tangent of the angle 0.

Applicant lists below the successive log values a of S and F and their first differences in the following table;

AS s F AF This table shows the obtained values in terms of log area for S and F. AS is the diflerence between the first'two entries under S, i. e.

and 2.96-*2. 62=.34, etc. Since these differences are log differences and are approximately linear accomplished at great expense of time and labor they may be represented by the equation y=mz+b. If we solve for m and b, F can be substituted for u and S for a: andthen there is obtained F=K'S+C', where F is the log area of the matching far Judgment; Sis the judgment of the stereo-area seen'through the instrument and 01s a constant- From the data of the above table we may write =mS+b Solving for m 5.02=3.46m+b 4.91=2.96m+b Subtracting .11= .50m

and Q x m: .22 Solving for b:

F= .22S+b 5.02=.22 (3.46) +b 5.02: fls-l-b b= 4.26

Substituting for m and b Equation F=.22S+4.26 indicates that for this individual, if the phenomenal stereo-area is multiplied by .22 adding to this product 4.26, the logarithm of the matching area is obtained. Since the points defining the line a in Figure 11 were actually made in the field, and since the equation enables applicant to transform the stereo-data into the field data with satisfactory accuracy, it is justifiable to make theprevious assertion with regard to the feasibility of this method of transforming stereo-measurements into the expected field measurements.

In addition to the field and stereo-curves a and b, Figure 11 also shows, in-light dot-dash lines, curves d and e which represent characteristics conforming to the so-called Emmerts Law, and based on the mathematical considerations discussed hereinbefore. It will be noted that curves (1 and b do not conform to'the results which should have been obtained according to Emmerts Law, and as a matter of fact my determinations have shown that Emmerts Law could not possibly hold. This law states that the pro- Jection area of an object varies inversely as the second power of the distance. Ii the same object is seen at twice the distance, it should appear one-fourth as large. Generally far objects are seen too large, and near objects are seen too small. This is the principle which Thouless has called phenomenal regression to reality. -It is also known as the principle of size-constancy. The apparent size of any object depends, therefore, not only upon its distance from the eye but also, upon a set of laws relating to its background surroundings.

The curves a and b which were obtained by actual field and instrument test, conclusively show that Emmerts Law, as pertaining to the subject of stereo-vision, does not hold. Some of the devices of the prior art operate on. the principles enunciated by this law and for that reason do not give a correct determination or diagnosis of a patients eyes considered from the stereopsis standpoint. On the other hand, the principles incorporated in the improved instrument which i make with the beam I This change ward or away from the observer.

aseaecv tion which must be added to the other optical I for-convenience may termed astereo-discorrection factors at the lenses in order that the parator, are based on"-": oth actual'field tests under carefully controlled and ideal conditions and determinations obtained in a laboratory emfplcying an accurate instrument of the; type described. v

tis. apparent that the angles which the bars distan objects in the :field as :translated"*into -,a

' corresponding increased distance "effect-provided byytheoptical systemof the instrument. It'will e understood that the i by an observer in thefield' may be simulatedgby providing the correct focusing'lenses at the veyepieces 6 of the instrument. Theadjustment at the knob 20 by which the bars]lareeithermoved 9 may have to bechanged toa'ccommodate changes in; the focal lengths orthelenses inserted at the'eye-pieces 6, (Figure l).- in an'gularity, in efiect, compensates for the smaller angles subtended by the{ more distance "efiectsas viewed normal stereo-vision may, if" desired, becom able lenses may be prescribed to give the-proper of operating the same which are capable fof-"re-J outwardly or inwardly aboutth elr pivots fl pro-- vides' the necessary change in rate, of movement of the charts 3|, either inwardly or outwardly, to correspond with thechange in the-subtended angle asthe observed object is moved either to- While I have described the improved stereodisparator from the standpoint of diagnosinglthe stereovision of a patient tosimulate actual field tests, it will be understood that the. instrument parisons may be made in determining the'shapes may also-be employed to advantage to develop fusional skill and sharp focusing in the various When the device is employed for matic lenses have been installed in the eye-pieces 21 is then moved either forwarder backward until the images become either blurred or separated, showing that the patient does not have the correct stereo-vision at 'thefield distances corresponding to the optical distances of theiinstrument .i The plate 2| isthen moved to its initial position, afterwhich it is again moved to its second position and if thisprocess is repeated at number of times, assuming thatthe eyes have no organic defects,.'the;stereoevision'ofthe pai tient will' have improved at','*least-' to jsuch an I extent that he will be able completely 't'o fuse the two images at the second position as .well as he did at the first position of the plate. I

:The plate is then moved to' a position such that the depth perception, efiectsare' again 10st,; then-f alternately moving the,plateito one of the 1 positions at which the stereo-vision is --apparen t All of these steps are repeated, moving the plate jihendr within y invention such modificat as representing the stereoscopic complementsof one i range of the patients stereo-lvisioncapabillty, and then restoring the plate tojthe patientsfstereovision position, and it willflbefound; after con-' tinued practice that the'patient'will have estab lished binocular vision throughoutthe entireileld distance as simulated by the opticalisystemof the instrument. This training method may also be appliedto the vertical movements of the ref spective charts until the ocular 'irnbalanceor ex -g to one another when said holder is moved f along cess phorias in the vertical]direction ha e,been" eliminated. If it is'assumed that tlie,in tr'u.--.v

. ment curve I represents the normal stereo yor binocularvision of a subject, any deviation from i this curve at any point would representjxacorrecthe eyes of the subject under test. I

measure of phenomenal psychological size (as tance relations.

I strument, said attachment including asuppo v which is slidably mounted a picture-holder caj pictures with respect to one another when said Znamed means including means-for moving the. V v pictures longitudinally of the line of-sight and for simultaneously moving them transversely I away from, or toward each otheras I moved respectively away from; or:- towardi' the co .2! back and forth untilit move'sjust out of the w strumentQsaid attachment including 1a support;

' carrying a pair of"spaced-pictures, lsaid pictures optical instrument, andmeans on the; support the line ot'sightand for simultaneously moving." I them transverselyaway from or towardeach stereo-vision of that subject will conform to the standard curve b. These corrections may be set out in any suitable manner as a' prescription similar to the prescriptions in the case of ordi nary eye diagnoses. The corrective factors'shown by the instrument to be necessarydn providing bined with other corrective factors so that suitcombined magnifying and stereoscopic powerI-to I From the-foregoing it is evident-that I have disclosed an improved instrument and methods vealing to the ophthalmologistanditheoptome-I trist anomalies of near-point and far-point vision not possible with any knownoptical' device. The, improved stereo disparator has-been operated under practicalconditions and hasjbeenfound j to give extremely accurate diagnosis of the stereo or tri-dimensionalvision of a patient. While I have described the invention more par,- ticularly on the basis-of comparing phenomenal areas of a target, it'will be understood that other discriminating characteristics from .which com-r and positions of the curves a and b (Figure Ill can be employed for measuring stereopsis. For, example, I may utilize to advantage an objective distinguished from area), form; position anddisv It will be understood that I desire to come] comewithin the scope of'the claims and the n vention. c Having thus fully described my 1 v tm t wh I claim as new and'desire to secure by Letter Patent,is: I, l. A device for testing binocular vision com prising an attachmentfor a standard optical rying a pair of spaced pictures, said pictures another and adapted to be viewed through saidi optical instrument, and means On the support coacting with said holder and said pictures for" automatically and simultaneously moving said holder is moved along said support, said last they. are

viewer in a longitudinal direction.

2. A device for testing-binocular; vis o e prising an attachment for a standard; optical in:

on which is slidably mounted azpicture holder representing the stereoscopic complements' 'o one another and adapted tobe viewed through'sa" c'oacting with said holder and said picturesior automatically moving said pictures with respect.

said support, said last-named means including means for moving the pictures longitudinally go f;

other as they are moved respectively away from or toward the viewer in a longitudinal direction.

3. A device for testing binocular vision comprising a binocular lens structure adapted to be focused and carried on a support which extends along the line of sight, a pair of spaced stereo-- scopic pictures, a holder carrying said pictures and slidably mounted on said support, said pictures adapted to be fused into a single image when viewed through said lens structure; said pictures being movable as a unit along said line of sight, means on the'support coacting with said holder and said pictures for automatically moving said pictures with respect to one another as the pictureunit is moved along the line of sight,

said last-named means including means for moving the pictures longitudinally of the line of sight and for simultaneously moving them transversely away from or ,toward each other as they are moved respectively away from or toward the viewer in a longitudinal direction.

4. A device for testing binocular vision comprising a pair of lenses spaced apart the normal interocular distance, a picture holder positioned in front of said lenses and movable with respect thereto, said holdercontaining a pair of spaced pictures which are the binocular complement of one another and adapted to be viewed stereoscopically through said lenses, means on the support coacting with said holder and said pictures for changing the spacing between the pictures as the holder is moved with respect tov the lenses, said means comprising a guideway on said device, and a guide on at least one of said pictures which cooperates with said guideway for simultaneously moving the pictures away from or toward each other as they are moved respectively away from or toward the viewer in a longitudinal direction.

5. A device for testing binocular vision comprising a pair of lenses spaced apart the normal interocular distance, a picture holder positioned said means comprising a guideway on said device,

and a guide on at least one of said pictures which cooperates with said guideway for simultaneously moving the pictures away from or toward each other as they are moved respectively away from or toward the viewer in a longitudinal direction, said guideway being positioned at an angle with tures as the holder is moved with respect to the lenses, said means comprising a pair of guide-' ways on opposite sides of the median line of sight of said lenses, and guides on said pictures which bear respectively against said guideways to cause the pictures to recede from one another while maintaining their planar relation as the picture holder is moved away from said lenses, said guideways extending away from one another as viewed from said lenses whereby the pictures are caused to approach one another as the distance from said lens to said pictures is decreased.

8. A device for testing binocular vision comprising a support which extends along the viewing direction, a picture holder slidably mounted on said support, a pair of spaced pictures movably mounted on said holder, said support having a tapered guideway at each side thereof, a pair of pin adapted slidably to engage said guideway and means connecting each pin to a picture whereby the pictures are moved longitudinally of the line of sight and simultaneously moved transversely away from or toward each other as they are moved respectively away from or toward the viewer in a longitudinal direction.

9. A device for testing binocular vision comprising a support which extends alongthe viewing direction, a picture holder slidably mounted on said support, a pair of spaced pictures movably mounted on said holder, and an opening in each picture, said support having a tapered guideway at each side thereof, a pair of pins adapted slidably to engage said guideway, a pair of bars, means slidably upporting said bars, each pin being mounted on a bar,'means connecting each bar to a picture whereby the pictures are moved longitudinally of the line of sight and simultaneously moved transversely away from or toward each other as they are moved respectively away from or toward the viewer in a longitudinal direction.

10. A device for testing binocular vision comprising an attachment for an optical instrument,

respect to the median line of sight of said lenses.

6. A device for testing binocular vision comprising a pair of lenses spaced apart the normal interocular distance, a picture holder positioned in front of said lenses andmovable with, respect thereto, said holder containing a pair of spaced pictures positioned in a single plane and which are the binocular complement of one another and adapted to be viewed stereoscopically through said lenses, means coacting with said holder for changing the spacing between the pictures as the holder is moved with respect to the lenses, said means comprising a pair of guideways on opposite sides of the median line of sight of said lenses, and guides on said pictures which bear respectively against said guideways to cause the pictures to recede from one another while mainsaid attachment including a support on which is slidably mounted a picture holder, 9. picture mounted in said picture holder, a cradle for each of said pictures, said cradle being mounted on said picture holder and adapted to move in a .vertical direction with respect thereto, means including a screw accessory for elevating the cradle whereby the picture is moved in a vertical direction, and means including a tapered guideway secured to said support, means engaging said guideway and attached to a picture whereby the pictures are moved longitudinally of the line of sight and simultaneously moved transversely away from or toward each other as they are moved respectively away from or toward. the viewer in a longitudinal direction.

11. A device for testing binocular vision comprising an attachment for an optical instrument, said attachment including a support on which is mounteda picture holder, a pair of spaced for adjusting the angle with which said bars extend with respect to said support.

12. A device for testing binocular vision comprising an attachment for an optical instrument,

said attachment including a support on which is mounted a picture holder, a pair of spaced pictures movably mounted on said holder, said support having a pair of bars at each side thereof, said bars forming a triangular shape the base of which is positioned remote from the optical inrotated in either direction the bars are caused to swing about their pivots thus to change the angularity of the bars with respect to said support. q

14; A device for testing binocular vision comprising an attachment for an optical instrument, said attachment including a support on which is slidably mounteda picture holder carrying a pair of spaced pictures, said pictures representing the stereoscopic complement of one another and adapted to be viewed through said optical instrument, means for moving said pictures with respect to one another when said holder is moved along aid support, said means comprising a pair strument, guides secured respectively to said pictures and so arranged that they will contact the guiding surfaces of said bars whereby as the holder is moved with respect to the optical instrument the pictures are caused to recede or approach one another depending on the direction in whichthe picture holder is moved, and means for adjusting the angle with which said bars extend with respect to said support, said means comprising a rod spanning-said bars and extending in the same direction as the triangular base formed by the bars, said rod having oppositely threaded portions which engage projections on said bars and cause the latter to move either outwardly or inwardly with respect to one another and thereby change the angle which the bars make with said support.

13. A device for testing binocular vision comprising an attachment for an optical instrument, said attachment including a support on which is slidably mounted a picture holder carrying a pair of spacedpictures, said pictures representing the stereoscopic complement of one another and adapted to be viewed through said optical instrument, means for moving said pictures with respect to one another when saidholder is movedalong said support, said means comprising a pair of port, said bars being pivotally. mounted at the base of the formed triangle on a support and being spaced apart at the apex of the formed of bars positioned on opposite sides of said support and extending angularly with respect to said support, said bars being pivotally mounted at the base of the formed triangle on a. support and being spaced apart at the apex of the formed a triangle by a tension spring, means for adjusting the angularity of the bars with respect to said support, said last-mentioned means comprising a rod having oppositely threaded portions which are received by projections on said bars, the arrangement being such that as the rod is rotated in either direction the bars are caused to swing about their pivots thus to change the angularity of the bars with respect to said support, and pins bearing along the outer surfaces of said bars, said pins being connected to said pic-tures whereby as the picture holder is moved along its support the pictures are caused to recede from or approach one another depending on the direction in which the picture holder is moved and at a rate determined by the angularity given said bars due to the position of said rod.

15. A device for testing depth perception comprising a lens viewing piece carried on a support which extends along the line of sight of said lens,

- a carriag slidably mounted on said support and carrying a picture holder, a pair of spaced stereoscopic pictures in the holder, said. holder being provided with a. trough-shaped support at the lower edge on which the picture is mounted and also being provided with a looped upper edge to support the picture in the vertical plane, the interior width of said picture holder being greater than the width or the pictures, and means coacting with said holder and with said picture for moving the pictures independently of one another the holder, said last-named means including means for moving the pictures longitudinally of the line of sight and for simultaneously moving them transversely away from or I toward each other as they are moved respectively away from or toward the viewer in a longitudinal direction.

, SAMUEL RENSHAW. 

